[RFC PATCH v2 2/8] iomap: add dma-buf direct I/O guards

[Mengmeng Zhao]

From: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>

Direct I/O copies data from the CPU in four places, zero-filling
holes, inline data, bounce pages and integrity metadata. A dma-buf
iterator has no pages behind it, so refuse it there.

Reads that encounter a hole or unwritten extent therefore return
-EOPNOTSUPP for the entire operation, even if I/O for an earlier
mapped extent was already submitted.

Signed-off-by: Nitesh Shetty <nj.shetty@xxxxxxxxxxx>
Signed-off-by: Anuj Gupta <anuj20.g@xxxxxxxxxxx>
Signed-off-by: Mengmeng Zhao <zhaomengmeng@xxxxxxxxxx>
Signed-off-by: Li Wang <liwang@xxxxxxxxxx>
---
 fs/iomap/direct-io.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index ad041ac3252a..4a2b0f9df5a7 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -425,6 +425,11 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 	unsigned int alignment;
 	ssize_t ret = 0;
 
+	/* integrity metadata is generated from the data pages */
+	if (iov_iter_is_dmabuf_map(dio->submit.iter) &&
+	    (iomap->flags & IOMAP_F_INTEGRITY))
+		return -EOPNOTSUPP;
+
 	/*
 	 * File systems that write out of place and always allocate new blocks
 	 * need each bio to be block aligned as that's the unit of allocation.
@@ -589,7 +594,13 @@ static int iomap_dio_bio_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 
 static int iomap_dio_hole_iter(struct iomap_iter *iter, struct iomap_dio *dio)
 {
-	loff_t copied = iov_iter_zero(iomap_length(iter), dio->submit.iter);
+	loff_t copied;
+
+	/* zero-filling walks the data pages */
+	if (iov_iter_is_dmabuf_map(dio->submit.iter))
+		return -EOPNOTSUPP;
+
+	copied = iov_iter_zero(iomap_length(iter), dio->submit.iter);
 
 	if (dio->flags & IOMAP_DIO_FSBLOCK_ALIGNED) {
 		loff_t aligned_copied = round_down(copied,
@@ -619,6 +630,10 @@ static int iomap_dio_inline_iter(struct iomap_iter *iomi, struct iomap_dio *dio)
 	loff_t pos = iomi->pos;
 	u64 copied;
 
+	/* inline data is copied from the CPU */
+	if (iov_iter_is_dmabuf_map(iter))
+		return -EOPNOTSUPP;
+
 	if (WARN_ON_ONCE(!inline_data))
 		return -EIO;
 
@@ -717,6 +732,10 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	if (!iomi.len)
 		return NULL;
 
+	/* bouncing copies the data from the CPU */
+	if (iov_iter_is_dmabuf_map(iter) && (dio_flags & IOMAP_DIO_BOUNCE))
+		return ERR_PTR(-EOPNOTSUPP);
+
 	dio = kmalloc_obj(*dio);
 	if (!dio)
 		return ERR_PTR(-ENOMEM);
-- 
2.43.0